Synthetic gas, or syngas, may be produced by reacting solid or liquid carbonaceous fuels with gases such as air, enriched air, or oxygen, in the optional presence of steam or water in a gasification reactor. The syngas obtained is withdrawn from the gasification reactor and subjected to several cleansing operations to rid it of various contaminants which are formed or liberated from the solid or liquid carbonaceous fuels during the gasification operation. These contaminants can readily become environmental pollutants if not properly treated during the gasification operation.
For example, materials often found in the syngas include hydrogen sulfide, ammonia, cyanides, phenols, various halogens and particulates in the form of carbon, ash, and coal, as well as trace metals. The disposal and control of these pollutants must be satisfactorily handled in order to make gasification a viable process without suffering attendant pollution problems.
As the syngas is discharged from the gasifier, it is usually subjected to multiple cooling and cleaning operations involving a scrubbing technique wherein the gas is introduced into at least one scrubber and is contacted with a water spray which cools the gas and condenses such condensables as tar, oil and organics. The water used for the scrubbing operation becomes what is commonly known as "black water," since it is contaminated with carbon. This black water can also contain soluble gases. This black water may be subjected to a variety of steps which may include the decantation of the carbon-containing solids, the partial concentration of solids in the slurry, the stripping of such gases as hydrogen sulfide, ammonia, and also solvent extraction steps to remove the carbon and dissolved carbon-containing compounds such phenols and cyanides.
Particulate solids, i.e. carbon, soot, and ash, entrained in the hot raw gas stream from a partial oxidation gas generator are removed by quench cooling the hot gas stream directly in water in a quench drum and by scrubbing with water in a gas scrubbing zone. By this means, a clean gas stream and a dispersion of particulate solids i.e. carbon and ash are produced. It is economic to reclaim the water in the aforesaid dispersion by removing particulate solids and gaseous impurities. However, in the reclaiming operation troublesome pumpable aqueous emulsions form in the system and have to be removed. The reclaimed water may be then recycled to the gas quench cooling and scrubbing zone.
Prior art utilized a flash column for reclamation of gray water. Gray water is water that has had a substantial fraction of the carbon and other solids removed. These systems are not able to remove a sufficient quantity of the noxious gases to allow open atmospheric treatment of the degassed black water.